Cooling device for helium



Gfls BUFFER 10 March 7, 1967 KUPPlNG 3,307,370

COOLING DEVICE FOR HELIUM Filed Aug. 6, 1965 5 12 I /X kvzowm nm MPRES.I C} E G I 1 c; i? I I I I i l I 22 23 24 4 Lpcguenm lr /enlor: GUSTAVuppme,

Atfomeas United States Patent Office 3,307,370 Patented Mar. 7, 1967 8Claims. 61. 62-210) The present invention relates generally to therefrigeration art and, more particularly, to a helium refrigeratorwherein the liquid helium from the sump of a helium liquefying device isfed to an externally located consumption device and the gas pumped outof the latter is recycled through the liquefying device.

In the cryogenic art, a refrigerator is understood to mean acontinuously operating refrigerating plant for producing lowtemperatures in the range of 2.5 to 30 K. Such a plant has as aparticular characteristic thereof that the liquid vapor mixture (e.g.,hydrogen or helium) collecting downstream from the expansion valve isfed in its entirety to the consumer or cryostat, and that the cold gasobtained in the consumer is refed, in accordance with its temperature,into the low pressure portion of one of the lower counter-current heatexchangers in the liquefying device.

The advantage of this cryogenic system resides in the higherrefrigerating power of the plant produced with the same mechanical poweras employed for a liquefying device. The consumer utilizes not only theevaporation energy of the liquid refrigerating medium, but also theenthalpy of the cold gas resulting from the temperature difference whenentering and exiting from the consumer. The further refrigeration powerin the gas is almost completely utilized in the liquefying device bymeans of the cold gas recycling process.

At higher operating temperatures, correspondingly higher amounts ofrefrigeration energy may be supplied to the consumer or, in other words,the refrigeration energy available for the consumer becomes smaller whenapproaching the boiling point of the refrigerating medium.Correspondingly, refrigerators are employed most advantageously in caseswhere large amounts of refrigeration energy are required and wherecontinuous operation is indispensable. However, there are also providedrefrigerators for small amounts of refrigeration energy at highertemperature, for example, 1 w. at 20 K., for the cooling of amplifierelements.

With operating temperatures above the boiling point of the refrigeratingmedium, the consumer is generally located outside of the liquefyingdevice. With operating temperatures below the boiling point, however, afluid 'bath at the desired temperature is usually produced within theliquefying device, i.e., the sample to be cooled is inserted into theliquefying device.

A disadvantage of known refrigerators is that they have littleflexibility with respect to the operating conditions, e. g., temperatureand refrigeration energy.

At operating temperatures above the boiling point of the refrigeratingmedium, the inlet wherein the cold gas is refed into the liquefyingdevice is selected in such a manner that the temperature in theliquefying. device at this inlet corresponds to the temperature of thereturning gas. Certain variations may be obtained by providing severalinlets in the liquefying device which can be used selectively. However,the construction of the countercurrent heat exchangers must be adaptedto accommodate the quantity of cold gas produced in the consumer. Thismeans that a refrigerator in each case must be adapted for theparticular operating conditions.

At operating temperatures below the boiling point of the refrigeratingmedium, the conditions are even more unfavorable. Here, the temperatureof the fluid bath present in the sump of the liquefying device whereinthe sample is inserted is lowered below the boiling point by decreasingthe pressure above the liquid. In order to cool the fluid bath to 25 K.,for example, the pressure above the boiling liquid must be decreasedfrom 760 mm. Hg to 77 mm. Hg. This is accomplished by removing the gaswhich is produced by pumping it, by means of an externally locatedvacuum pump connected to the low pressure gas exit of the liquefyingdevice, through the counter-current heat exchangers. Thus, the pressurein the entire low pressure portion of the liquefying device is loweredto a pressure corresponding to the desired temperature or to a stilllower pressure determined by the flow resistance. In order to achieve asufliciently small flow resistance of the counter-current heatexchangers and a sufficient heat exchange in these counter-current heatexchangers, the heat exchangers must be specially constructed for thedesired operating conditions. Thus, a refrigerator of conventionaldesign possesses very little flexibility with regard to operatingtemperature and refrigerating power at operating temperatures below theboiling point of the refrigerating medium.

An object of this invention is the provision of a refrigeratorarrangement having great flexibility with regard to operatingtemperature and refrigerating power.

Another object of this invention is the provision of thermostaticallyoperating valves for regulating the flow to and from the consumerwhereby a desired temperature is maintained within the consumer.

A further object is to provide a high efficiency refrigerator system fortemperatures below 42 K. wherein the need for auxiliary refrigerant inthe consumer is eliminated.

In order to overcome the disadvantages of the prior refrigerator systemsencountered in producing low temperatures, this invention provides athermostatically operated valve in the liquid refrigerant supply linefor regulating the flow of the liquid refrigerant from the liquefyingdevice to the consumer, which is a continuous flow cryostat, inaccordance with the temperature at a selected point within thecontinuous flow cryostat. The thermostatically operated valve ispreferably located at the inlet of the supply line in the sump of theliquefying device. A vacuum pump for removing the gas from thecontinuous flow cryostat is connected to the continuous flow cryostatvia another thermostatically operated valve which is also controlled inaccordance with the temperature at a selected point within thecontinuous flow cryostat. The vacuum pump is connected to a compressorthrough a gas buffer which equalizes the volume of gas flowing to thecompressor, the compressor in turn feeding the liquefying device andproviding a cyclic operation. This invention also provides for thesupply line from the liquefying device to the continuous flow cryostatto function as a throttle path whereby the supply line operates tomaintain an excess pressure in the low pressure portion of theliquefying device, as is necessary for the normal liquefier operation,and to maintain in the evaporator a pressure 'below one atmosphere,corresponding to the desired temperature below 4.2 K., the pressure droptaking place in the supply line for the liquid refrigerant.

Additional objects and advantages of the present invention will becomeapparent upon consideration of the following description when taken inconjunction with the accompanying drawing in which a schematic view of asystem constructed in accordance with the present invention isillustrated.

With more particular reference to the drawing the helium refrigeratorsystem comprises a helium liquefier 2 supplied with high pressure gas bya compressor 1. The liquefier comprises in addition to an engine (notshown), several counter-current heat exchangers 21, 22., 23, as well asa Joule-Thomson expansion valve 24. The system further comprises a feedline for the liquid refrigerant 3 having a liquid control valve 4 and athrottle path 5 connecting the liquefier 2 to a continuous flow cryostat6. The continuous flow cryostat 6 and the throttle path 5 may be of thetype shown in co-pending US. application Serial No. 396,556, filedSeptember 16, 1964, now Patent No. 3,279,214 for Pump. The continuousflow cryostat 6 is provided with an exhaust gas line 7 which isconnected via a gas regulating valve 8 to a vacuum pump 9, a gas buffer10 and to the compressor 1. The gas buffer 10 may be selectivelyinserted into the system via valves 11 and 12 to equalize the volume ofexhaust gas supplied to the compressor. A gas supply 14 shown as bottledgas is connected to the gas buffer 10 through a valve 13. The regulatingvalves 4 and 8 are connected, via lines 15 and 16, with one or moretemperature sensing elements provided at a selected point withincryostat 6, whereby the liquid regulating valve 4 controls the supply ofliquid to the continuous flow cryostat 6 and the gas regulating valve 8controls the pressure or temperature, respectively, in the cryostat.

In operation, the refrigerator is first cooled down by feeding gaseoushelium from the gas supply 14 via the gas buffer 10 and the compressor 1into the liquefying device wherein the helium is liquefied. When thesump of the liquefier 2 is filled with liquid helium, the liquid controlValve 4 is opened with the vacuum pump 9 operating and liquid helium isconducted via the throttle path 5 into the continuous flow cryostat 6where it evaporates under normal pressure or under reduced pressure,thereby effecting the desired cooling to the desired temperature.

After the desired temperature has been reached, the operation of thethermostatically controlled valves 4 and 8 commences in dependence uponthe temperature of the continuous flow cryostat 6, whereby thetemperature of the cryostat is kept constant. The adjustment to anyother desired temperatures may be effected during operation by adjustingthe control valves 4 and 8. The refrigerant whose refrigerating contentcan be completely utilized in the continuous fiow cryostat 6 is thenrecycled, in gaseous form, from the vacuum pump to the suction side ofthe compressor 1.

During the operation of the plant, the preferred operating pressure formaintaining equilibrium of the plant is a pressure of approximately 1.2atmospheres in the low pressure portion of the liquefier 2, and atoperating temperatures below 42 K., there is simultaneously provided apressure below 1.0 atmosphere in the continuous flow cryostat 6 whichcorresponds to the desired temperature.

Thus, it is noted that in the refrigerator system of this invention, theliquid helium is conducted from the sump of the liquefying device, bymeans of a vacuum pump, into a continuous flow cryostat where itevaporates and effects the desired cooling. The constant temperature inthe continuous flow cryostat is regulated by regulating the feed ofliquid by means of a control valve in the supply line for the liquidrefrigerant, which valve is thermostatically controlled in dependenceupon the temperature in the cryostat and by controlling the pressure inthe cryostat via a control valve in the exhaust line which is likewisecontrolled in dependence upon the temperature in the cryostat, in athermostatic manner. The gaseous helium conveyed by the vacuum pump isconducted, selectively via the gas buffer, to the compressor whichsupplies the helium liquefying device with the required high pressuregas.

The advantage of such a refrigerator arrangement resides particularly inits great flexibility, with respect to the temperature to be produced,as well as with respect to the refrigerating energy available for theconsumer. In accordance with the invention, it is possible to employtemperatures in the continuous flow cryostat which are below as well asabove 4.2 K. and to vary the temperature during operation without thedanger of the liquefying device and the entire system losingequilibrium. The stored liquid in the sump of the liquefying devicerepresents a reserve in refrigeration energy, i.e., the refrigeratingpower taken therefrom can also vary within wide limits, or can besubjected to variations during operation. When setting temperaturesbelow 42 K., only the continuous flow cryostat is maintained underdecreased pressure, while the low pressure portion of the liquefyingdevice is, as usual,

under a slight excess pressure. Thus, conventional helium liquefyingdevices can be employed for operating the proposed refrigerator devicewithout special constructional alterations which is particularlyadvantageous. A further advantage of the device is that considerablyhigher refrigeration energy is available for the consumer, because theentire refrigeration content of the cold helium gas can be utilized inthe continuous flow cryostat, i.e., up to room temperature. Therefore,an auxiliary refrigerant such as liquid nitrogen, which is normallyindispensable in the refrigerator operation to cool the radiation shieldof the consumer may be eliminated. The radiation shield of thecontinuous flow cryostat is cooled with cold exhaust gas.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

What is claimed is:

1. A cryogenic gas refrigerator system using a refrigerant, comprising,in combination:

a compressor;

liquifier means connected to said compressor for liquefying arefrigerant;

a continuous flow cryostat connected to said liquefier means forproducing controllable low temperatures by evaporation of the liquidrefrigerant;

first thermostatically controlled valve means for regulating the flow ofthe liquefied refrigerant between said liquefier means and saidcontinuous flow cryostat in response to the temperature at a pointwithin said cryostat;

a vacuum pump connected between said continuous flow cryostat and saidcompressor for pumping the gas from said cryostat to said compressor;and

second thermostatically controlled valve means for regulating the flowof the gas between said continuous flow cryostat and said vacuum pump inresponse to the temperature at a point within said cryostat.

2. A system as defined in claim 1 comprising means for supplying arefrigerant in gaseous form to said compressor.

3. A system as defined in claim 2 further comprising:

a first fluid conveying means connected between said liquefier and saidcontinuous flow cryostat;

a second fluid conveying means connected between said cryostat and saidpump; and

a third fluid conveying means connected between said pump and saidcompressor, including a gas buffer volume in a by-pass line.

4. A system as defined in claim 3 wherein said means for supplyingrefrigerant in gaseous form is connected to said third fluid conveyingmeans via said gas buffer volume for supplying an equalized volume ofgas to said compressor.

5. A system as defined in claim 3 wherein said liquefier means isprovided with a sump wherein the liquefied refrigerant is stored;

said first fluid conveying means having an inlet located in said sump;and

said first thermostatically controlled valve means being connected tosaid first fluid conveying means at said inlet.

6. A system as defined in claim 3 wherein said first fluid conveyingmeans provides a throttle path for said liquefied refrigerant forproducing a reduction in pressure between said liquefier means and saidcontinuous flow cryostat.

7. A system as defined in claim 6 wherein equilibrium is maintained insaid system at a desired temperature below 42 K., by providing:

a first pressure slightly in excess of one atmosphere in the lowpressure portion of said liquefier means; and

a second pressure below one atmosphere in said continuous flow cryostat,said second pressure corresponding to the desired temperature; wherebysaid first fluid conveying means provides the reduction in pressurebetween said liquefier means and said cryostat.

8. A cryogenic helium refrigerator system for temperatures below 42 I(.,comprising:

a compressor;

means for supplying helium in gaseous form to said compressor;

liquefier means connected to said compressor for liquefying said helium,said liquefier means having a low pressure portion wherein a pressureslightly in excess of one atmosphere is maintained and a sump forstoring the liquid helium;

a continuous flow cryostat for producing controllable low temperaturesby evaporation of said liquid helium said cryostat having temperaturesensing means therein, and in said cryostat a pressure below oneatmosphere being maintained;

first fluid conveying means having an inlet in said sump connectedbetween said liquefier means and said continuous flow cryostat, saidfirst fluid conveying means providing a throttle path wherein areduction in pressure is produced between said liquefier means and saidcryostat;

first thermostatically controlled valve means provided at the inlet ofsaid first fluid conveying means for regulating the flow of said liquidhelium through said first fluid conveying means in response to saidtemperature sensing means;

a vacuum pump for removing the helium gas originating in said continuousflow cryostat from said cryostat and supplying said gas to saidcompressor;

second fluid conveying means connected between said cryostat and saidvacuum pump;

second thermostatically controlled valve means provided within saidsecond fluid conveying means for regulating the flow of said gas throughsaid second fluid conveying means in response to said temperaturesensing means; and

third fluid conveying means connected between said vacuum pump and saidcompressor, comprising a gas buffer volume in a by-pass line forequalizing the volume of gas supplied to said compressor if necessary,said third fluid conveying means having connected thereto, via said gasbufier volume, said means for supplying helium in gaseous form to saidcompresssor.

References Cited by the Examiner UNITED STATES PATENTS 3,162,716 12/1964Silver 62514 3,200,613 8/1965 Zotos 62467 X 3,250,079 5/1966 Davis 629MEYER PERLIN, Primary Examiner.

1. A CRYOGENIC GAS REFRIGERATOR SYSTEM USING A REFRIGERANT, COMPRISING,IN COMBINATION: A COMPRESSOR; LIQUIFIER MEANS CONNECTED TO SAIDCOMPRESSOR FOR LIQUEFYING A REFRIGERANT; A CONTINUOUS FLOW CRYOSTATCONNECTED TO SAID LIQUEFIER MEANS FOR PRODUCING CONTROLLABLE LOWTEMPERATURES BY EVAPORATION OF THE LIQUID REFRIGERANT; FIRSTTHERMOSTATICALLY CONTROLLED VALVE MEANS FOR REGULATING THE FLOW OF THELIQUEFIED REFRIGERANT BETWEEN SAID LIQUEFIER MEANS AND SAID CONTINUOUSFLOW CRYOSTAT IN RESPONSE TO THE TEMPERATURE AT A POINT WITHIN SAIDCRYOSTAT; A VACUUM PUMP CONNECTED BETWEEN SAID CONTINUOUS FLOW CRYOSTATAND SAID COMPRESSOR FOR PUMPING THE GAS FROM SAID CRYOSTAT TO SAIDCOMPRESSOR; AND SECOND THERMOSTATICALLY CONTROLLED VALVE MEANS FORREGULATING THE FLOW OF THE GAS BETWEEN SAID CONTINUOUS FLOW CRYOSTAT ANDSAID VACUUM PUMP IN RESPONSE TO THE TEMPERATURE AT A POINT WITHIN SAIDCRYOSTAT.